In continuous ink jet printing apparatus streams of uniformly spaced ink drops are created by imposing predetermined vibrations upon liquid ink filaments issuing from an orifice plate. The filaments are formed by supplying ink under pressure to a print head cavity that is in communication with the orifice plate. Information is imparted to the droplet streams by selective noncharging or charging and deflection of droplets. A portion of the droplets pass to the recording medium but there are a substantial number of non-printing droplets that are intercepted by a catcher for recirculation. Often the print head cavity has an outlet other than the orifice plate (e.g. to facilitate dynamic pressure control within the cavity at startup), and the apparatus ink supply system also circulates such ink flow.
Typically continuous ink jet printers include a large ink reservoir, to and from which ink is circulated by a pump. The reservoir is often maintained at subatmospheric pressure by a vacuum pump to effect return of ink from the print head and/or catcher. U.S. Pat. No. 4,314,264 discloses one such ink circulation system and it will be appreciated that a multicolor printing apparatus can have a plurality of these systems. In such printers, it is very important that ink for one color system not be introduced into another and vice versa. In addition, inks are generally water-based or solvent-based and it is equally catastrophic if those two ink types are inadvertently intermixed.
There are many opportunities for incorrect ink mistakes to happen because ink must be replenished to the circulation system fairly frequently. Similar problems exist for circulation systems wherein the main ink reservoir is a removable ink cartridge, e.g. see U.S. Pat. No. 4,591,875. To avoid the coupling of improper ink cartridges to the circulation systems of a multicolor printer, U.S. Pat. No. 4,853,708 provides a keyed, apparatus-ink cartridge interface system. In that system each housing of the printer is fitted with its own unique pin configuration and cartridges having a particular ink are formed with plug and hole configurations such that the cartridge will interfit only in the proper housing.
The concept described in the `708 patent is very useful; however, it would be desirable to have systems of this kind that are improved from the viewpoints of simplicity of fabrication and assembly and to provide more tolerance in the interfit interfaces of the printer housing and ink supply module.